The present invention relates to the treatment of water in a cooling system such as that employed in the air conditioning apparatus of a building. Such systems commonly include heat exchangers through which cooling water flows, the water being cooled by partial evaporation in air as the water falls by gravity within a cooling tower which is usually mounted on the roof of the building.
Three main impurity problems are encountered in the treatment of water in cooling systems including a cooling tower. The first significant problem is fouling of the system which is caused by the growth of algae and slime caused by bacteria and fungi. Such fouling reduces both water flow and heat transfer efficiency. Until recently, the recognized method of controlling algae, scaling and corrosion has been to employ a variety of chemical additives. A broad range of chemicals have been required to keep these contaminants under control. Constant care and changing of the type of chemicals has been a necessity for maintaining algae free systems. This is time consuming and extremely costly, and additionally creates an environmental hazard due to dumping of excessive chemicals to sewerage or storm drain systems.
The second significant impurity problem is corrosion. Over a period of time, corrosion due to organic secretion and decay will require extensive repair and replacement of costly equipment. Corrosion control chemicals are equally difficult to maintain due to various types of corrosion problems. Chemicals such as alkaline chromates are effective in reducing all types of corrosion. However, they are extremely dangerous and highly toxic compounds, which necessitate secondary bleed water treatment processes before the bleed water is allowed to be dumped. This is an extremely expensive process.
The third significant impurity problem, and by far the most common problem, is scaling. Scaling is caused by the deposition of dissolved minerals on the cooling tower baffles and particularly on the hot surface areas in the condenser tubes of the heat exchanger where heat transfer is most important.
Current methods of solving scale problems are to reduce the total dissolved solids in the system. One method is by increasing the bleed water rate; however, this is very expensive in areas where water supply costs and sewage charges are expensive. Dissolved solids in water build up to a limit where no more material can be dissolved in water. At this limit, the addition of further material will cause either a sludge or scale to form. Controlling cycles of concentration in the recirculating water is customarily done by bleeding off sump water until a satisfactory limit of solids in the water is reached.
Another method of preventing scale is to reduce the hardness and alkalinity of water by supplying the cooling tower with softened water through the ion exchange process. However, the high usage of salt in the brine solution used to regenerate the water softeners causes this method to be chemical intensive and expensive. Polysphosphates may be introduced into the system for sequestering the calcium and magnesium minerals so that they don't precipitate out as scale formation. This is also an expensive method of scale control and adds to the total dissolved solids factor on a molecular ratio of one to one. Polyphosphate treatment is also controlled by the ph factor; higher ph values above 8.5 tend to reduce its effectiveness and consequently an increase in bleed off rate is required which adds a further cost.
Other treatment processes have been tried from time to time with varying degrees of success. A variety of filtration type products have been tried. Electromagnetic descaling devices, permanent magnetic descaling devices and catalytic type scale inhibitor devices have also been employed. Ozone generating devices have been utilized for introducing ozone into the recirculating water. However, these various processes taken either alone or in combination with one another have not been able to provide the ultimate goal of providing a cooling system which eliminates the necessity of adding chemicals to the system with the attendant problems, and further which eliminates the requirement of bleeding water to the system thereby providing a zero bleed system.